Bruton's Tyrosine Kinase (BTK), a member of the non-receptor tyrosine kinase Tec family, is a key signaling enzyme expressed in all types of hematopoietic cells other than T lymphocytes and natural killer cell, and plays a crucial role in the B cell signaling pathway that binds a B-cell receptor (BCR) on surface of cells to stimulate the cellular response downstream.
BTK is a key regulator for B cell development, activation, signaling and survival (Kurosaki, Curr Op Imm, 2000, 276-281; Schaeffer and Schwartzberg, Curr Op Imm 2000, 282-288). In addition, BTK plays a role among many signaling pathways of hematopoietic cells in addition to the B cell signaling pathway, such as Toll-like receptor (TLR) and cytokine receptor-mediated TNF-α production in macrophages, immunoglobulin E receptor (FcεRI) signaling in mast cells, inhibition of Fas/APO-1 cell apoptosis in B-lineage lymphoid cells and collagen-stimulated platelet aggregation.